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Eric Paris5444e292009-12-17 21:24:27 -05001/*
2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2, or (at your option)
7 * any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; see the file COPYING. If not, write to
16 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19/*
20 * fsnotify inode mark locking/lifetime/and refcnting
21 *
22 * REFCNT:
Lino Sanfilippo9756b912013-07-08 15:59:46 -070023 * The group->recnt and mark->refcnt tell how many "things" in the kernel
24 * currently are referencing the objects. Both kind of objects typically will
25 * live inside the kernel with a refcnt of 2, one for its creation and one for
26 * the reference a group and a mark hold to each other.
27 * If you are holding the appropriate locks, you can take a reference and the
28 * object itself is guaranteed to survive until the reference is dropped.
Eric Paris5444e292009-12-17 21:24:27 -050029 *
30 * LOCKING:
Lino Sanfilippo9756b912013-07-08 15:59:46 -070031 * There are 3 locks involved with fsnotify inode marks and they MUST be taken
32 * in order as follows:
Eric Paris5444e292009-12-17 21:24:27 -050033 *
Lino Sanfilippo9756b912013-07-08 15:59:46 -070034 * group->mark_mutex
Eric Paris5444e292009-12-17 21:24:27 -050035 * mark->lock
Eric Paris5444e292009-12-17 21:24:27 -050036 * inode->i_lock
37 *
Lino Sanfilippo9756b912013-07-08 15:59:46 -070038 * group->mark_mutex protects the marks_list anchored inside a given group and
39 * each mark is hooked via the g_list. It also protects the groups private
40 * data (i.e group limits).
41
42 * mark->lock protects the marks attributes like its masks and flags.
43 * Furthermore it protects the access to a reference of the group that the mark
44 * is assigned to as well as the access to a reference of the inode/vfsmount
45 * that is being watched by the mark.
Eric Paris5444e292009-12-17 21:24:27 -050046 *
47 * inode->i_lock protects the i_fsnotify_marks list anchored inside a
48 * given inode and each mark is hooked via the i_list. (and sorta the
49 * free_i_list)
50 *
51 *
52 * LIFETIME:
53 * Inode marks survive between when they are added to an inode and when their
54 * refcnt==0.
55 *
56 * The inode mark can be cleared for a number of different reasons including:
57 * - The inode is unlinked for the last time. (fsnotify_inode_remove)
58 * - The inode is being evicted from cache. (fsnotify_inode_delete)
59 * - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
60 * - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
61 * - The fsnotify_group associated with the mark is going away and all such marks
62 * need to be cleaned up. (fsnotify_clear_marks_by_group)
63 *
64 * Worst case we are given an inode and need to clean up all the marks on that
65 * inode. We take i_lock and walk the i_fsnotify_marks safely. For each
66 * mark on the list we take a reference (so the mark can't disappear under us).
67 * We remove that mark form the inode's list of marks and we add this mark to a
Lino Sanfilippo9756b912013-07-08 15:59:46 -070068 * private list anchored on the stack using i_free_list; we walk i_free_list
69 * and before we destroy the mark we make sure that we dont race with a
70 * concurrent destroy_group by getting a ref to the marks group and taking the
71 * groups mutex.
72
Eric Paris5444e292009-12-17 21:24:27 -050073 * Very similarly for freeing by group, except we use free_g_list.
74 *
75 * This has the very interesting property of being able to run concurrently with
76 * any (or all) other directions.
77 */
78
79#include <linux/fs.h>
80#include <linux/init.h>
81#include <linux/kernel.h>
Eric Paris75c1be42010-07-28 10:18:38 -040082#include <linux/kthread.h>
Eric Paris5444e292009-12-17 21:24:27 -050083#include <linux/module.h>
84#include <linux/mutex.h>
85#include <linux/slab.h>
86#include <linux/spinlock.h>
Eric Paris75c1be42010-07-28 10:18:38 -040087#include <linux/srcu.h>
Eric Paris5444e292009-12-17 21:24:27 -050088
Arun Sharma600634972011-07-26 16:09:06 -070089#include <linux/atomic.h>
Eric Paris5444e292009-12-17 21:24:27 -050090
91#include <linux/fsnotify_backend.h>
92#include "fsnotify.h"
93
Eric Paris75c1be42010-07-28 10:18:38 -040094struct srcu_struct fsnotify_mark_srcu;
95static DEFINE_SPINLOCK(destroy_lock);
96static LIST_HEAD(destroy_list);
97static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
98
Eric Paris5444e292009-12-17 21:24:27 -050099void fsnotify_get_mark(struct fsnotify_mark *mark)
100{
101 atomic_inc(&mark->refcnt);
102}
103
104void fsnotify_put_mark(struct fsnotify_mark *mark)
105{
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200106 if (atomic_dec_and_test(&mark->refcnt)) {
107 if (mark->group)
108 fsnotify_put_group(mark->group);
Eric Paris5444e292009-12-17 21:24:27 -0500109 mark->free_mark(mark);
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200110 }
Eric Paris5444e292009-12-17 21:24:27 -0500111}
112
113/*
114 * Any time a mark is getting freed we end up here.
115 * The caller had better be holding a reference to this mark so we don't actually
116 * do the final put under the mark->lock
117 */
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200118void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
119 struct fsnotify_group *group)
Eric Paris5444e292009-12-17 21:24:27 -0500120{
Eric Paris0d48b7f2009-12-17 21:24:27 -0500121 struct inode *inode = NULL;
Eric Paris5444e292009-12-17 21:24:27 -0500122
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200123 BUG_ON(!mutex_is_locked(&group->mark_mutex));
124
Lino Sanfilippo104d06f2011-06-14 17:29:48 +0200125 spin_lock(&mark->lock);
Eric Paris5444e292009-12-17 21:24:27 -0500126
Eric Paris700307a2010-07-28 10:18:38 -0400127 /* something else already called this function on this mark */
128 if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
Eric Paris5444e292009-12-17 21:24:27 -0500129 spin_unlock(&mark->lock);
Lino Sanfilippoe2a29942011-06-14 17:29:51 +0200130 return;
Eric Paris5444e292009-12-17 21:24:27 -0500131 }
132
Eric Paris700307a2010-07-28 10:18:38 -0400133 mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
134
Eric Paris0d48b7f2009-12-17 21:24:27 -0500135 if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
Eric Paris0d48b7f2009-12-17 21:24:27 -0500136 inode = mark->i.inode;
Eric Parisb31d3972010-04-21 16:49:38 -0400137 fsnotify_destroy_inode_mark(mark);
Eric Paris0d48b7f2009-12-17 21:24:27 -0500138 } else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
139 fsnotify_destroy_vfsmount_mark(mark);
Eric Paris5444e292009-12-17 21:24:27 -0500140 else
141 BUG();
142
143 list_del_init(&mark->g_list);
Eric Paris5444e292009-12-17 21:24:27 -0500144
Eric Paris5444e292009-12-17 21:24:27 -0500145 spin_unlock(&mark->lock);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200146
Lino Sanfilippo6960b0d2011-08-12 01:13:31 +0200147 if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
148 iput(inode);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200149 /* release lock temporarily */
Lino Sanfilippo986ab092011-06-14 17:29:50 +0200150 mutex_unlock(&group->mark_mutex);
Eric Paris5444e292009-12-17 21:24:27 -0500151
Eric Paris75c1be42010-07-28 10:18:38 -0400152 spin_lock(&destroy_lock);
153 list_add(&mark->destroy_list, &destroy_list);
154 spin_unlock(&destroy_lock);
155 wake_up(&destroy_waitq);
Lino Sanfilippo6960b0d2011-08-12 01:13:31 +0200156 /*
157 * We don't necessarily have a ref on mark from caller so the above destroy
158 * may have actually freed it, unless this group provides a 'freeing_mark'
159 * function which must be holding a reference.
160 */
Eric Paris75c1be42010-07-28 10:18:38 -0400161
Eric Paris5444e292009-12-17 21:24:27 -0500162 /*
163 * Some groups like to know that marks are being freed. This is a
164 * callback to the group function to let it know that this mark
165 * is being freed.
166 */
167 if (group->ops->freeing_mark)
168 group->ops->freeing_mark(mark, group);
169
170 /*
171 * __fsnotify_update_child_dentry_flags(inode);
172 *
173 * I really want to call that, but we can't, we have no idea if the inode
174 * still exists the second we drop the mark->lock.
175 *
176 * The next time an event arrive to this inode from one of it's children
177 * __fsnotify_parent will see that the inode doesn't care about it's
178 * children and will update all of these flags then. So really this
179 * is just a lazy update (and could be a perf win...)
180 */
181
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200182 atomic_dec(&group->num_marks);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200183
Lino Sanfilippo6960b0d2011-08-12 01:13:31 +0200184 mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200185}
186
187void fsnotify_destroy_mark(struct fsnotify_mark *mark,
188 struct fsnotify_group *group)
189{
Lino Sanfilippo6960b0d2011-08-12 01:13:31 +0200190 mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200191 fsnotify_destroy_mark_locked(mark, group);
192 mutex_unlock(&group->mark_mutex);
Eric Paris5444e292009-12-17 21:24:27 -0500193}
194
Eric Paris90b1e7a2009-12-17 21:24:33 -0500195void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
196{
197 assert_spin_locked(&mark->lock);
198
199 mark->mask = mask;
200
201 if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
202 fsnotify_set_inode_mark_mask_locked(mark, mask);
203}
204
Eric Paris33af5e32009-12-17 21:24:33 -0500205void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
206{
207 assert_spin_locked(&mark->lock);
208
209 mark->ignored_mask = mask;
210}
Eric Paris90b1e7a2009-12-17 21:24:33 -0500211
Eric Paris5444e292009-12-17 21:24:27 -0500212/*
213 * Attach an initialized mark to a given group and fs object.
214 * These marks may be used for the fsnotify backend to determine which
215 * event types should be delivered to which group.
216 */
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200217int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
218 struct fsnotify_group *group, struct inode *inode,
219 struct vfsmount *mnt, int allow_dups)
Eric Paris5444e292009-12-17 21:24:27 -0500220{
221 int ret = 0;
222
Eric Paris5444e292009-12-17 21:24:27 -0500223 BUG_ON(inode && mnt);
224 BUG_ON(!inode && !mnt);
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200225 BUG_ON(!mutex_is_locked(&group->mark_mutex));
Eric Paris5444e292009-12-17 21:24:27 -0500226
227 /*
Eric Paris5444e292009-12-17 21:24:27 -0500228 * LOCKING ORDER!!!!
Lino Sanfilippo986ab092011-06-14 17:29:50 +0200229 * group->mark_mutex
Lino Sanfilippo104d06f2011-06-14 17:29:48 +0200230 * mark->lock
Eric Paris5444e292009-12-17 21:24:27 -0500231 * inode->i_lock
232 */
Lino Sanfilippo104d06f2011-06-14 17:29:48 +0200233 spin_lock(&mark->lock);
Eric Paris700307a2010-07-28 10:18:38 -0400234 mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
235
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200236 fsnotify_get_group(group);
Eric Paris5444e292009-12-17 21:24:27 -0500237 mark->group = group;
238 list_add(&mark->g_list, &group->marks_list);
239 atomic_inc(&group->num_marks);
240 fsnotify_get_mark(mark); /* for i_list and g_list */
241
242 if (inode) {
243 ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
244 if (ret)
245 goto err;
Eric Paris0d48b7f2009-12-17 21:24:27 -0500246 } else if (mnt) {
247 ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
248 if (ret)
249 goto err;
Eric Paris5444e292009-12-17 21:24:27 -0500250 } else {
251 BUG();
252 }
253
Eric Paris90b1e7a2009-12-17 21:24:33 -0500254 /* this will pin the object if appropriate */
255 fsnotify_set_mark_mask_locked(mark, mark->mask);
Eric Paris5444e292009-12-17 21:24:27 -0500256 spin_unlock(&mark->lock);
257
258 if (inode)
259 __fsnotify_update_child_dentry_flags(inode);
260
261 return ret;
262err:
Eric Paris700307a2010-07-28 10:18:38 -0400263 mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
Eric Paris5444e292009-12-17 21:24:27 -0500264 list_del_init(&mark->g_list);
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200265 fsnotify_put_group(group);
Eric Paris75c1be42010-07-28 10:18:38 -0400266 mark->group = NULL;
Eric Paris5444e292009-12-17 21:24:27 -0500267 atomic_dec(&group->num_marks);
Eric Paris5444e292009-12-17 21:24:27 -0500268
Eric Paris5444e292009-12-17 21:24:27 -0500269 spin_unlock(&mark->lock);
270
Eric Paris75c1be42010-07-28 10:18:38 -0400271 spin_lock(&destroy_lock);
272 list_add(&mark->destroy_list, &destroy_list);
273 spin_unlock(&destroy_lock);
274 wake_up(&destroy_waitq);
275
Eric Paris5444e292009-12-17 21:24:27 -0500276 return ret;
277}
278
Lino Sanfilippod5a335b2011-06-14 17:29:52 +0200279int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
280 struct inode *inode, struct vfsmount *mnt, int allow_dups)
281{
282 int ret;
283 mutex_lock(&group->mark_mutex);
284 ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
285 mutex_unlock(&group->mark_mutex);
286 return ret;
287}
288
Eric Paris5444e292009-12-17 21:24:27 -0500289/*
Eric Paris4d926042009-12-17 21:24:34 -0500290 * clear any marks in a group in which mark->flags & flags is true
Eric Paris5444e292009-12-17 21:24:27 -0500291 */
Eric Paris4d926042009-12-17 21:24:34 -0500292void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
293 unsigned int flags)
Eric Paris5444e292009-12-17 21:24:27 -0500294{
295 struct fsnotify_mark *lmark, *mark;
Eric Paris5444e292009-12-17 21:24:27 -0500296
Lino Sanfilippo6960b0d2011-08-12 01:13:31 +0200297 mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
Eric Paris5444e292009-12-17 21:24:27 -0500298 list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
Eric Paris4d926042009-12-17 21:24:34 -0500299 if (mark->flags & flags) {
Eric Paris4d926042009-12-17 21:24:34 -0500300 fsnotify_get_mark(mark);
Lino Sanfilippo64c20d22011-06-14 17:29:53 +0200301 fsnotify_destroy_mark_locked(mark, group);
302 fsnotify_put_mark(mark);
Eric Paris4d926042009-12-17 21:24:34 -0500303 }
Eric Paris5444e292009-12-17 21:24:27 -0500304 }
Lino Sanfilippo986ab092011-06-14 17:29:50 +0200305 mutex_unlock(&group->mark_mutex);
Eric Paris5444e292009-12-17 21:24:27 -0500306}
307
Eric Paris4d926042009-12-17 21:24:34 -0500308/*
309 * Given a group, destroy all of the marks associated with that group.
310 */
311void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
312{
313 fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
314}
315
Eric Paris5444e292009-12-17 21:24:27 -0500316void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
317{
318 assert_spin_locked(&old->lock);
319 new->i.inode = old->i.inode;
320 new->m.mnt = old->m.mnt;
Lino Sanfilippo23e964c2011-06-14 17:29:47 +0200321 if (old->group)
322 fsnotify_get_group(old->group);
Eric Paris5444e292009-12-17 21:24:27 -0500323 new->group = old->group;
324 new->mask = old->mask;
325 new->free_mark = old->free_mark;
326}
327
328/*
329 * Nothing fancy, just initialize lists and locks and counters.
330 */
331void fsnotify_init_mark(struct fsnotify_mark *mark,
332 void (*free_mark)(struct fsnotify_mark *mark))
333{
Eric Parisba643f02009-12-17 21:24:27 -0500334 memset(mark, 0, sizeof(*mark));
Eric Paris5444e292009-12-17 21:24:27 -0500335 spin_lock_init(&mark->lock);
336 atomic_set(&mark->refcnt, 1);
Eric Paris5444e292009-12-17 21:24:27 -0500337 mark->free_mark = free_mark;
338}
Eric Paris75c1be42010-07-28 10:18:38 -0400339
340static int fsnotify_mark_destroy(void *ignored)
341{
342 struct fsnotify_mark *mark, *next;
David Cohenefa8f7e2014-06-04 16:05:42 -0700343 struct list_head private_destroy_list;
Eric Paris75c1be42010-07-28 10:18:38 -0400344
345 for (;;) {
346 spin_lock(&destroy_lock);
Andreas Gruenbacher8778abb2010-07-28 10:18:38 -0400347 /* exchange the list head */
348 list_replace_init(&destroy_list, &private_destroy_list);
Eric Paris75c1be42010-07-28 10:18:38 -0400349 spin_unlock(&destroy_lock);
350
351 synchronize_srcu(&fsnotify_mark_srcu);
352
353 list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
354 list_del_init(&mark->destroy_list);
355 fsnotify_put_mark(mark);
356 }
357
358 wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
359 }
360
361 return 0;
362}
363
364static int __init fsnotify_mark_init(void)
365{
366 struct task_struct *thread;
367
368 thread = kthread_run(fsnotify_mark_destroy, NULL,
369 "fsnotify_mark");
370 if (IS_ERR(thread))
371 panic("unable to start fsnotify mark destruction thread.");
372
373 return 0;
374}
375device_initcall(fsnotify_mark_init);